Genetic polymorphisms in older subjects with vascular or Alzheimer's dementia

Angiotensin-converting enzyme polymorphisms AND Alzheimer's disease susceptibility: An updated meta-analysis

Background

Many studies among different ethnic populations suggested that angiotensin converting enzyme (ACE) gene polymorphisms were associated with susceptibility to Alzheimer’s disease (AD). However, the results remained inconclusive. In the present meta-analysis, we aimed to clarify the effect of ACE polymorphisms on AD risk using all available relevant data.

Methods

Systemic literature searches were performed using PubMed, Embase, Alzgene and China National Knowledge Infrastructure (CNKI). Relevant data were abstracted according to predefined criteria.

Results

Totally, 82 independent cohorts from 65 studies were included, focusing on five candidate polymorphisms. For rs1799752 polymorphism, in overall analyses, the insertion (I) allele conferred increased risk to AD compared to the deletion (D) allele (I vs. D: OR = 1.091, 95% CI = 1.007–1.181, p = 0.032); while the I carriers showed increased AD susceptibility compared with the D homozygotes (II + ID vs. DD: OR = 1.131, 95% CI = 1.008–1.270, p = 0.036). However, none of the positive results passed FDR adjustment. In subgroup analysis restricted to late-onset individuals, the associations between rs1799752 polymorphism and AD risk were identified using allelic comparison (OR = 1.154, 95% CI = 1.028–1.295, p = 0.015, FDR = 0.020), homozygotes comparison, dominant model and recessive model (II vs. ID + DD: OR = 1.272, 95% CI = 1.120–1.444, p < 0.001, FDR < 0.001). Nevertheless, no significant association could be revealed after excluding studies not in accordance with Hardy-Weinberg equilibrium (HWE). In North Europeans, but not in East Asians, the I allele demonstrated increased AD susceptibility compared to the D allele (OR = 1.096, 95% CI = 1.021–1.178, p = 0.012, FDR = 0.039). After excluding HWE-deviated cohorts, significant associations were also revealed under homozygotes comparison, additive model (ID vs. DD: OR = 1.266, 95% CI = 1.045–1.534, p = 0.016, FDR = 0.024) and dominant model (II + ID vs. DD: OR = 1.197, 95% CI = 1.062–1.350, p = 0.003, FDR = 0.018) in North Europeans. With regard to rs1800764 polymorphism, significant associations were identified particularly in subgroup of European descent under allelic comparison (T vs. C: OR = 1.063, 95% CI = 1.008–1.120, p = 0.023, FDR = 0.046), additive model and dominant model (TT + TC vs. CC: OR = 1.116, 95% CI = 1.018–1.222, p = 0.019, FDR = 0.046). But after excluding studies not satisfying HWE, all these associations disappeared. No significant associations were detected for rs4343, rs4291 and rs4309 polymorphisms in any genetic model.

Conclusions

Our results suggested the significant but modest associations between rs1799752 polymorphism and risk to AD in North Europeans. While rs4343, rs4291 and rs4309 polymorphisms are unlikely to be major factors in AD development in our research.

Genetic Variants and Oxidative Stress in Alzheimer's Disease

In an aging society, the number of people suffering from Alzheimer's Disease (AD) is still growing. Currently, intensive research is being carried out on the pathogenesis of AD. The results of these studies indicated that oxidative stress plays an important role in the onset and development of this disease. Moreover, in AD oxidative stress is generated by both genetic and biochemical factors as well as the functioning of the systems responsible for their formation and removal. The genetic factors associated with the regulation of the redox system include TOMM40, APOE, LPR, MAPT, APP, PSEN1 and PSEN2 genes. The most important biochemical parameters related to the formation of oxidative species in AD are p53, Homocysteine (Hcy) and a number of others. The formation of Reactive Oxygen Species (ROS) is also related to the efficiency of the DNA repair system, the effectiveness of the apoptosis, autophagy and mitophagy processes as well as the antioxidant potential. However, these factors are responsible for the development of many disorders, often with similar clinical symptoms, especially in the early stages of the disease. The discovery of markers of the early diagnosis of AD may contribute to the introduction of pharmacotherapy and slow down the progression of this disease.

Genetic architecture of common non-Alzheimer's disease dementias

Frontotemporal dementia (FTD), dementia with Lewy bodies (DLB) and vascular dementia (VaD) are the most common forms of dementia after Alzheimer's disease (AD). The heterogeneity of these disorders and/or the clinical overlap with other diseases hinder the study of their genetic components. Even though Mendelian dementias are rare, the study of these forms of disease can have a significant impact in the lives of patients and families and have successfully brought to the fore many of the genes currently known to be involved in FTD and VaD, starting to give us a glimpse of the molecular mechanisms underlying these phenotypes. More recently, genome-wide association studies have also pointed to disease risk-associated loci. This has been particularly important for DLB where familial forms of disease are very rarely described. In this review we systematically describe the Mendelian and risk genes involved in these non-AD dementias in an effort to contribute to a better understanding of their genetic architecture, find differences and commonalities between different dementia phenotypes, and uncover areas that would benefit from more intense research endeavors.

Methylenetetrahydrofolate reductase C667T polymorphism and susceptibility to late-onset Alzheimer's disease in the Italian population

INTRODUCTION

This study is a meta-analysis of the published studies on the relationship between methylenetetrahydrofolate reductase (MTHFR) C667T polymorphism and the risk of late- onset Alzheimer 's disease (LOAD) in Italian cohorts.

EVIDENCE ACQUISITION

We conducted a search on the electronic databases PubMed/Medline, Web of Science and Scopus. All cohort and case-control studies investigating the association between MTHFR 677T polymorphism and LOAD in Italian population published any time to May 8, 2020 were included in the analysis.

EVIDENCE SYNTHESIS

From an initial screening of 136 articles, 4 were included into the systemic review. The pooled analysis based on the co-dominant model revealed that the MTHFR C677T polymorphism was associated with a significant risk of LOAD among Italian cohorts (TC vs. CC: OR=1.20, 95% CI=1.06-1.36, P=0.004, I²=0%). Conversely, the pooled analysis based on the allelic model demonstrated a non-significant relationship between the MTHFR C677T polymorphism and susceptibility to LOAD in Italians (OR: 1.25, 95% CI: 0.99-1.59, P=0.060, I²=14.6%). Moreover, Italian subjects with MTHFR 677TT genotype resulted to have a significantly increased susceptibility to LOAD (OR=1.75, 95% CI=1.23-2.50, P=0.002, I²=0%).

CONCLUSIONS

The present meta-analysis showed only trend of association between MTHFR C677T polymorphism and LOAD in Italian population; however, it also demonstrated an increased susceptibility of LOAD in patients having MTHFR 677TT genotype. Further studies are needed to establish whether MTHFR polymorphisms can be used as non-invasive biomarker for LOAD.

The C677T Polymorphism of the Methylenetetrahydrofolate Reductase Gene and Susceptibility to Late-onset Alzheimer's Disease

Folate metabolism makes a crucial contribution towards late-onset Alzheimer's disease (LOAD). Moreover, methylenetetrahydrofolate reductase (MTHFR) constitutes the primary enzyme of the folate pathway. We hypothesize that there is an association of C677T polymorphism in the MTHFR gene with the susceptibility to LOAD. Previous published research has investigated the link between the MTHFR C677T polymorphisms and LOAD susceptibility; nevertheless, the findings have continued to be not only controversial, but also indecisive. Accordingly, we carried out the present meta-analysis for the assessment of the potential link that exists between the MTHFR C677T polymorphism and the susceptibility to LOAD. Furthermore, we carried out a literature search of the PubMed, EMBASE, Cochrane Library, and WanFang database up to August 10, 2018. The odds ratios (ORs) with the respective 95% confidence interval (95%CI) were put to use for the evaluation of the robustness of the link of the MTHFR C677T polymorphism with the vulnerability to LOAD. All statistical analyses were carried out using STATA 15.0. An aggregate of 14 case-control research works was retrieved, involving 2,467 LOAD patients as well as 2,877 controls. We found that a substantial link exists between C677T polymorphism and LOAD risk in a codominant framework (TC vs. CC: OR=1.22, 95%CI=1.00-1.49, P=0.049). In addition to the stratified analysis based on ethnicity, which suggested that C677T polymorphism was likely linked only to an augmented threat of LOAD in Asians, it did not exist among Caucasians. Furthermore, in the subgroup analysis carried out using APOE ɛ4 status, a substantial increase in the susceptibility to LOAD was detected in APOE ɛ4 carriers as well as non-APOE ɛ4 carriers. In sum, the current meta-analysis revealed that MTHFR C677T polymorphism was associated with susceptibility to LOAD. Further extensive case-control studies are required.

A Meta-Analysis on the Relationship of the PON Genes and Alzheimer Disease

AIM

This study aimed to evaluate the association of the paraoxonase (PON) gene variants and Alzheimer disease (AD) using meta-analysis.

METHODS

Relevant studies were identified by searching English and Chinese databases extensively. Allele and genotype frequencies for each included study were extracted. Newcastle-Ottawa Scale (NOS) was employed to assess the quality of included studies. The odds ratio (OR) with 95% confidence interval (95% CI) was calculated using a random-effects or fixed-effects model. A Q statistic was used to evaluate homogeneity, and Egger test and funnel plot were used to assess publication bias.

RESULTS

A total of 15 studies (involving 5 polymorphisms) were included and identified for the current meta-analysis. The NOS scores ranged from 7 to 8, meaning good quality of studies. It was found that the SS genotype of PON2 S311C polymorphism had an significant association with AD in the studied population (OR = 0.82, 95% CI: 0.68-0.99, P = .04), and the A allele of PON1 rs705379 polymorphism was positively related to AD in Caucasian population (OR = 1.21, 95% CI: 1.05-1.39, P = .009) as well as the GG genotype decreased AD risk significantly in Caucasians (OR = 0.7, 95% CI: 0.56-0.88, P = .002). However, there was no significant relationship between other 3 genetic variants of PON genes (L55 M, Q192 R, and -161C/T of PON1 gene) and AD.

CONCLUSION

Existing evidence indicates that the S311C polymorphism (SS genotype) and the rs705379 (the A allele and GG genotype) are associated with risk of AD in studied population. Future studies with larger sample sizes will be necessary to confirm the present results.

Alzheimer's Disease and Paraoxonase 1 (PON1) Gene Polymorphisms

BACKGROUND

Some studies have indicated that human paraoxonase 1 (PON1) activity shows a polymorphic distribution. The aim of this study was to determine the distribution of PON1 polymorphism in patients with Alzheimer's disease in Gorgan and compare it with a healthy control group.

METHOD

The study included 100 healthy individuals and 50 patients. Enzyme activity and genetic polymorphism of PON1 were determined.

RESULT

There were significant differences in distribution of genotypes and alleles among patients and control group. The most common genotype was CT in patients and control group, while the most frequent alleles were T and C in patients and controls, respectively. There was a statistically significant variation between serum PON1 activity and -108C> T polymorphism. The highest PON1 enzyme activities in the patients and controls were found in CC, while lower enzyme activities were seen in CT and TT genotypes in both genders and age groups.

CONCLUSION

Onset of Alzheimer's disease may depend on different polymorphisms of the PON1 enzyme. Late or early-onset of Alzheimer's disease may also depend on age and gender distribution, especially for arylesterase enzyme. Further studies on polymorphism of the enzyme are necessary for interpretation of possible polymorphic effects of enzyme on PON1 activity in humans.

Genetics of vascular dementia - review from the ICVD working group

BACKGROUND

Vascular dementia is a common disorder resulting in considerable morbidity and mortality. Determining the extent to which genes play a role in disease susceptibility and their pathophysiological mechanisms could improve our understanding of vascular dementia, leading to a potential translation of this knowledge to clinical practice.

DISCUSSION

In this review, we discuss what is currently known about the genetics of vascular dementia. The identification of causal genes remains limited to monogenic forms of the disease, with findings for sporadic vascular dementia being less robust. However, progress in genetic research on associated phenotypes, such as cerebral small vessel disease, Alzheimer's disease, and stroke, have the potential to inform on the genetics of vascular dementia. We conclude by providing an overview of future developments in the field and how such work could impact patients and clinicians.

CONCLUSION

The genetic background of vascular dementia is well established for monogenic disorders, but remains relatively obscure for the sporadic form. More work is needed for providing robust findings that might eventually lead to clinical translation.

Homocysteine and Alzheimer's Disease: Evidence for a Causal Link from Mendelian Randomization

BACKGROUND/OBJECTIVE

The relationship between plasma homocysteine (Hcy) levels and Alzheimer's disease (AD) has been studied for many years, but remains controversial. While a recent meta-analysis of epidemiological studies, which included observational studies, indicated that homocysteine may be a risk factor for AD, there remains a need to further demonstrate this link due to the large degree of heterogeneity between studies. Epidemiological studies have certain limitations, as their results can be affected by confounding factors and reverse causation. In this study, we evaluated the relationship between plasma homocysteine and AD by using a Mendelian randomization method to avoid problems of confounding bias and reverse causality.

METHODS

We searched the PubMed and EMBASE databases for reports regarding the MTHFR C677T polymorphism (rs1801133) from the time of their inception to September 2015. These reports were combined with related observational studies, and used to evaluate the effect of MTHFR C677T (rs1801133) on the risk for AD. A recent meta-analysis of genome-wide association studies had previously suggested a relationship between homocysteine and MTHFR C677T (rs 1801133).

RESULTS

Our met-analysis included 34 studies with 9397 subjects, and demonstrated a significant relationship between plasma total homocysteine levels and the risk for AD (OR = 3.37; 95% CI = 1.90-5.95; p = 2.9×10-5).

CONCLUSION

Our meta-analysis demonstrated a causal link between plasma total homocysteine and the risk for AD, and provides a new insight into the etiology and prevention of AD.

Genetic and environmental factors in vascular dementia: an update of blood brain barrier dysfunction

Vascular dementia (VaD) describes a combination of both cognitive and behavioural manifestations associated with variable brain lesions of vascular origin. While vascular risk factors have been implicated in VaD, the relationship is most evident when the factors are considered together and not individually. This review will examine the significance of the integrity of blood brain barrier (BBB) tight junction (TJ) proteins - occludin and claudins in the pathophysiology of VaD. Specifically, some of the genetic contributors to VaD, namely those responsible for the integrity of the BBB, will be reviewed in detail. Moreover, environmental factors will be considered in conjunction with these genes to examine how the interaction of environmental and genetic factors contributes to one's susceptibility to VaD.

Potential Links between Impaired One-Carbon Metabolism Due to Polymorphisms, Inadequate B-Vitamin Status, and the Development of Alzheimer's Disease

Alzheimer's disease (AD) is the major cause of dementia and no preventive or effective treatment has been established to date. The etiology of AD is poorly understood, but genetic and environmental factors seem to play a role in its onset and progression. In particular, factors affecting the one-carbon metabolism (OCM) are thought to be important and elevated homocysteine (Hcy) levels, indicating impaired OCM, have been associated with AD. We aimed at evaluating the role of polymorphisms of key OCM enzymes in the etiology of AD, particularly when intakes of relevant B-vitamins are inadequate. Our review indicates that a range of compensatory mechanisms exist to maintain a metabolic balance. However, these become overwhelmed if the activity of more than one enzyme is reduced due to genetic factors or insufficient folate, riboflavin, vitamin B6 and/or vitamin B12 levels. Consequences include increased Hcy levels and reduced capacity to synthetize, methylate and repair DNA, and/or modulated neurotransmission. This seems to favor the development of hallmarks of AD particularly when combined with increased oxidative stress e.g., in apolipoprotein E (ApoE) ε4 carriers. However, as these effects can be compensated at least partially by adequate intakes of B-vitamins, achieving optimal B-vitamin status for the general population should be a public health priority.

Genetics of Vascular Dementia: Systematic Review and Meta-Analysis

BACKGROUND

Vascular dementia (VaD) is the second most common type of dementia. So far, little is known about the contribution of genetic polymorphisms to the risk of VaD. Many candidate genetic polymorphisms have been examined in a large number of studies. However, due to the conflicting results, the genetics of VaD is still behind the shadow.

OBJECTIVE

We conducted a comprehensive meta-analysis on associations between genetic polymorphisms of any gene and VaD to investigate the genetics of VaD.

METHOD

We sought the published studies of associations between any genetic polymorphism and VaD and critically appraised them. We assessed the effects of genetic models by calculating pooled odds ratios (ORs), investigating the origin of heterogeneity by subgroup analysis, and testing the robustness by random effect model and sensitivity analysis.

RESULTS

69 studies with 4,462 cases and 11,583 controls were included. We identified APOE ɛ2/ɛ3/ɛ4 and additional four genetic polymorphisms including MTHFR C677T, PON1 L55M, TGF-β1 +29C/T, and TNF-α -850C/T associated with VaD. Tested by random effect model and sensitivity analysis, the pooled results show nice robustness.

CONCLUSIONS

Our comprehensive meta-analysis highlighted the genetic contribution to sporadic VaD. Because of the small amount of data on associations between genetic polymorphisms, except for APOE, and VaD, more studies are needed to test the existing genetic polymorphisms and detect other related genetic variants.

Genetic susceptibility to vascular cognitive impairment: a pathophysiological view

The heterogeneity of the vascular cognitive impairment (VCI) creates challenges for research on its genetic basis and pathophysiology. Despite well-known monogenic forms may be useful to understand some pathogenic mechanisms leading to VCI, most of VCIs are sporadic disorders resulting from the interaction between environmental, vascular and genetic factors. Genetic investigation for VCI may encompass both candidate genes that affect critical biological processes to VCI and common and rare genetic variants identified across the entire genome study technology, thereby enabling us to confirm or expose new biological mechanisms in VCI and develop new therapeutic and preventive approaches. Notwithstanding genetic susceptibility to VCI remains largely unknown owing to methodological issues. Collaborative efforts emerge as an interesting strategy to overcome these problems.

Profile of the Paraoxonase 1 (PON1) Gene 192Q/R Polymorphism and Clinical Associations among Older Singaporean Chinese with Alzheimer's and Mixed Dementia

BACKGROUND

To examine the prevalence of the Paraoxonase1 (PON1) gene 192Q/R polymorphism amongst Singaporean Chinese with Alzheimer's disease (AD) and mixed dementia and possible clinical associations.

METHODS

We examined the presence of the PON1 192Q/R polymorphism together with cognitive status, functional status and neuropsychiatric symptoms among 186 older Singaporean Chinese with AD (n = 109) and mixed dementia (n = 77).

RESULTS

The R allele predominated in 67% of the AD patients and 63.1% of the patients with mixed dementia. Within the mixed dementia subgroup, the R allele was significantly associated with a higher BADLS score, NPI-Q scores and CDR scores.

CONCLUSION

Among older Singaporean Chinese with AD and mixed dementia, the R allele was predominant. In particular, within the mixed dementia subgroup, the R allele carrier status was associated with poorer functional status, greater presence of neuropsychiatric symptoms and a more severe stage of dementia. Further studies should be conducted.

Methylenetetrahydrofolate Reductase (MTHFR) C677T Polymorphism and Alzheimer Disease Risk: a Meta-Analysis

Methylenetetrahydrofolate reductase (MTHFR) is key enzyme of folate/homocysteine pathway. Case control association studies on MTHFR C677T polymorphism and Alzheimer's disease (AD) have been repeatedly performed over the last two decades, but the results are inconclusive. The aim of the present study was to assess the risk of MTHFR C677T polymorphism for AD. Forty-one studies were identified by a search of PubMed, Google Scholar, Elsevier, and Springer Link databases, up to January 2015. Odds ratios (ORs) with corresponding 95 % confidence interval (CI) were calculated using fixed effect model or random effect model. The subgroup analyses based on ethnicity were performed. MTHFR C677T polymorphism had a significant association with susceptibility to AD in all genetic models (for T vs C OR = 1.29, 95 % CI = 1.07-1.56, p = 0.003; for TT + CT vs CC OR = 1.29, 95 % CI = 1.19-1.40, p = 0.0004; for TT vs CC OR = 1.31, 95 % CI = 1.16-1.48, p = 0.001; for CT vs CC OR = 1.24, 95 % CI = 1.13-1.35, p < 0.004; and for TT vs CT + CC OR = 1.13, 95 % CI = 1.00-1.28, p = 0.02). Results of present meta-analysis supported that the MTHFR C677T polymorphism was associated with an increased risk of AD.

The MTHFR C677T polymorphism contributes to increased risk of Alzheimer's disease: evidence based on 40 case-control studies

The association between methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and Alzheimer's Disease (AD) risk has been widely reported with inconsistent results. We performed an updated meta-analysis of all available studies to clarify this situation. We conducted a comprehensive literature search in PubMed Alzgene, Embase, and Chinese Biomedical Literature database (CBM) for the period up to June 2014. Finally, a total of 40 case-control studies with 4503 AD cases and 5767 controls were included. Overall, significant increased AD risk was found, when all studies were pooled into the meta-analysis. In subgroup analyses stratified by ethnicity, age of onset, and APOE ϵ4 status, significant increased AD risk was found in Asians, late-onset AD, and APOE ϵ4 carriers, but not in Caucasians, early-onset AD, and non-APOE ϵ4 carriers. The present meta-analysis suggested that the MTHFR is a candidate gene for AD susceptibility. The MTHFR C677T polymorphism may be a risk factor for AD in Asians, APOE ϵ4 carriers, and late-onset AD. Further, investigations taking the potential gene-gene and gene-environmental interactions into consideration for the MTHFR C677T polymorphism should be conducted.

Angiotensin-converting enzyme insertion/deletion polymorphism is not a major determining factor in the development of sporadic Alzheimer disease: evidence from an updated meta-analysis

Angiotensin-converting enzyme gene (ACE) insertion/deletion (I/D) polymorphism have long been linked to sporadic Alzheimer disease (SAD), but the established data remained controversial. To clarify this inconsistency, a comprehensive meta-analysis was conducted. Through searching of Pubmed, Embase, Alzgene, China National Knowledge Infrastructure (CNKI) and manually searching relevant references, 53 independent studies from 48 articles were included, involving a total of 8153 cases and 14932 controls. The strength of association was assessed by using odds ratios (ORs) with 95% confidence intervals (CIs). Further stratified analyses and heterogeneity analyses were tested, as was publication bias. Overall, significant associations were revealed between I/D polymorphism and SAD risk using allelic comparison (OR = 1.09, 95%CI = 1.01–1.17, p = 0.030), homozygote comparison (OR = 1.17, 95%CI = 1.01–1.34, p = 0.030) and the dominant model (OR = 1.16, 95%CI = 1.04–1.29, p = 0.008), but they were not sufficiently robust to withstand the false-positive report probability (FPRP) analyses. Otherwise, in subgroup analyses restricted to the high quality studies, the large sample size studies and studies with population-based controls, no significant association was observed in any genetic models. In summary, the current meta-analysis suggested that the ACE I/D polymorphism is unlikely to be a major determining factor in the development of SAD.

Paraoxonase 1 in neurological disorders

Paroxonase 1 displays multiple physiological activities that position it as a putative player in the pathogenesis of neurological disorders. Here we reviewed the literature focusing on the role of paraoxonase 1 (PON1) as a factor in the risk of stroke and the major neurodegenerative diseases. PON1 activity is reduced in stroke patients, which significantly correlates inversely with carotid and cerebral atherosclerosis. The presence of the R allele of the Q192R PON1 polymorphism seems to potentiate this risk for stroke. PON1 exerts peroxidase activities that may be important in neurodegenerative disorders associated with oxidative stress. PON1 is also a key detoxifier of organophosphates and organophosphate exposure has been linked to the development of neurological disorders in which acetylcholine plays a significant role. In Parkinson's disease most of the studies suggest no participation of either L55M or the Q192R polymorphisms in its pathogenesis. However, many studies suggest that the MM55 PON1 genotype is associated with a higher risk for Parkinson's disease in individuals exposed to organophosphates. In Alzheimer's disease most studies have failed to find any association between PON1 polymorphisms and the development of the disease. Some studies show that PON1 activity is decreased in patients with Alzheimer's disease or other dementias, suggesting a possible protective role of PON1. No links between PON1 polymorphisms or activity have been found in other neurodegenerative diseases such as multiple sclerosis and amyotrophic lateral sclerosis. PON1 is a potential player in the pathogenesis of several neurological disorders. More research is warranted to ascertain the precise pathogenic links and the prognostic value of its measurement in neurological patients.

Complex genetic susceptibility to vascular dementia and an evidence for its underlying genetic factors associated with memory and associative learning

Genetic basis for vascular dementia (VD) as a typical complex disease has been limitedly reported from association studies conducted with candidate genes. Even recent genomewide association studies (GWAS) could hardly identify additional genetic factors for VD. Although a considerable complexity for its genetic architecture was suspected, there were some challenges to identify false negative associations that resulted from the GWAS. Challenges to identifying genetic factors and their functions after the trials of GWAS revealed that splicing of primary transcript was inhibited (SYK) or delayed (PHLDB2) by a nucleotide substitution of the corresponding gene. The studies gave us the lesson that integrated investigations with statistical genomics as well as functional genomics are needed to identify false negatives from the GWAS. Such endeavors would provide key insights into aspects of underlying nucleotide architectures of VD and incorporate the genetic factors into clinical practice. The recent genetic association studies for susceptibility to VD were briefly overviewed in this article. We also showed a challenge to understanding genetic dissection of VD by a genomic region enrichment analysis with distal cis-regulatory sequences. The analysis with a variant set of potential false negatives from the GWAS revealed that the variants were significantly enriched near genes involved in critical biological processes to VD.

Paraoxonase gene polymorphism and the risk for Alzheimer's disease in the polish population

BACKGROUND

The relationship between different paraoxonase (PON) gene polymorphisms and the risk of Alzheimer's disease (AD) was studied several times and the results were controversial.

METHODS

We investigated the association of 4 single-nucleotide polymorphisms (SNPs) of the PON1 (M55L; Q192R; -161C/T) and the PON2 (C311S) genes that were shown to affect the risk of sporadic AD. We studied 360 Caucasian cases with late-onset AD and 354 nondemented controls.

RESULTS

No significant differences were observed between the studied PON SNPs and AD risk. The results did not change after stratification of the apolipoprotein E status. Meta-analyses of studies in Caucasians assessing the associations between the PON1 M55L, -161C/T and Q192R SNPs and the risk of AD were performed, and no associations were found.

CONCLUSION

Our results suggest that the studied PON1 and PON2 polymorphisms are not associated with late-onset AD.

MTHFR (677 and 1298) and IL-6-174 G/C genes in pathogenesis of Alzheimer's and vascular dementia and their epistatic interaction

Genetic risk factors play an important role in the pathogenesis of Alzheimer disease (AD) and vascular dementia (VaD). In this case-control study, we examined C677T and A1298C (rs1801133 and rs1801131) polymorphism in the methylenetetrahydrofolate reductase (MTHFR) genes and their correlation with plasma levels of homocysteine (Hcy) in AD and VaD cases and evaluated the gene-gene interaction (epistasis) with IL-6-174 G/C (rs1800795). CC genotype was associated with elevated levels of plasma homocysteine (p = 0.004) as compared with genotype AA of rs1801131. In AD, we observed a significant (p = 0.04) association with C alleles of rs1801131. Regression analysis revealed that the presence of both rs1801133 T and rs1800795 C alleles increased the odds of developing AD by 2.5 and VaD by 3.7-fold. While rs1800795 (CC or GC) genotypes alone increased the odds of developing VaD by 2.2-fold, the presence of CC genotype of rs1801131 nullified this effect. The findings support the hypothesis that multiple genes are involved to alter the odds of developing AD and VaD.

Association between the MTHFR gene and Alzheimer's disease: a meta-analysis

BACKGROUND

The association between methylenetetrahydrofolate reductase (MTHFR) gene (rs1801133) 677C/T polymorphism and Alzheimer's disease (AD) is controversial. The objective of the study was to investigate the possible association between MTHFR 677C/T polymorphism and AD.

METHOD

We performed a meta-analysis pooling data from all relevant studies including 3,299 cases and 4,363 controls. We applied a random-effects or fixed-effects model to combine odds ratio (OR) and 95% confidence intervals (95% CI).

RESULTS

This meta-analysis demonstrated that the MTHFR T allele or dominant model for T allele (CT + TT) had an increased risk for AD in combined populations (OR, 95% CI: 1.13, 1.05-1.21; 1.18, 1.07-1.31, respectively), and a significant association was found in allele contrast, recessive, and dominant model in Asian populations, but not in Caucasian populations.

CONCLUSION

The MTHFR C677T polymorphism is associated with AD in Asian populations, but not in Caucasians.

Serum paraoxonase activity is associated with variants in the PON gene cluster and risk of Alzheimer disease

Previous studies have shown association of single nucleotide polymorphisms (SNPs) in 3 contiguous genes (PON1, PON2, and PON3) encoding paraoxonase with risk of Alzheimer disease (AD). We evaluated the association of serum paraoxonase activity measured by phenyl acetate (PA) and thiobutyl butyrolactone (TBBL) with risk of AD and with 26 SNPs spanning the PON gene cluster in 266 AD cases and 306 sibling controls from the MIRAGE study. The odds of AD (adjusted for age, gender, and ethnicity) increased 20% for each standard deviation decrease in PA or TBBL activity. There were association signals with activity in all 3 genes. Haplotypes including SNPs spanning the PON genes were generally more significant than haplotypes comprising SNPs from 1 gene. Significant interactions were observed between SNP pairs located across the PON cluster with either serum activity measure as the outcome, and between several PON SNPs and PA activity with AD status as the outcome. Our results suggest that low serum paraoxonase activity is a risk factor for AD. Furthermore, multiple variants in PON influence serum paraoxonase activity and their effects may be synergistic.

Meta-analysis of the methylenetetrahydrofolate reductase C677T polymorphism and susceptibility to Alzheimer's disease

No clear consensus has been reached at the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and Alzheimer's disease (AD) risk. Thus in this meta-analysis, a total of 19 case-control studies was assessed to evaluate the possible association. The data demonstrated that the frequency of T677 allele (T vs. C) was significantly associated with susceptibility to AD in all subjects (OR=1.15, 95% CI=1.06-1.26) and in East Asians (OR=1.22, 95% CI=1.08-1.39). There was statistical difference between AD patients and the controls under recessive genetic mode (CT+TT vs. CC) and homozygote comparison (TT vs. CC) in all subjects and in East Asians as well. Despite a small effect of the polymorphism on late-onset AD (LOAD) risk, MTHFR C677T polymorphism was not a major risk factor for LOAD in East Asians and Caucasians. A subgroup analysis in the subjects without APOE epsilon4 alleles showed T677 allele significantly increased risk of AD in all subjects (OR=1.21, 95% CI: 1.04-1.42) and in East Asians (OR=1.28, 95% CI: 1.06-1.55). However, no association was found in Caucasians. In conclusion, this meta-analysis supports that MTHFR C677T polymorphism is capable of causing AD susceptibility in East Asians, not in Caucasians.

Paraoxonase 1 polymorphisms are not related with the risk for multiple sclerosis

It has been suggested a possible role of oxidative stress and lipid peroxidation in the inflammatory processes and in the pathogenesis of multiple sclerosis. Human serum paraoxonase 1 is a polymorphic enzyme encoded by the gene PON1, located in chromosome 7q21.3, that plays a major role in the metabolism of organophosporus compounds, and in the protection against oxidative stress. Paraoxonase-1 activity has been found decreased in the plasma of multiple sclerosis patients. An association between PON1 polymorphism and the risk of multiple sclerosis has been described in Italians. To investigate the possible association between the PON1 genotype and allelic variants of the polymorphisms L55M and Q192R and the risk for multiple sclerosis in the Spanish Caucasian population; we studied the frequency of the PON1 genotypes and allelic variants in 228 patients with multiple sclerosis and 220 healthy controls using a PCR-RLFP method. The frequencies of the PON1 genotypes and allelic variants did not differ significantly between patients and controls, and were unrelated with gender, age of onset, and course of the disease. The OR (95% confidence intervals) for the variant alleles PON1-55L and PON1-192R were 0.96 (0.73-1.26) and 1.01 (0.76-1.35), respectively. The results of the present study suggest that PON1 polymorphism is not related with the risk for multiple sclerosis in our population.

The paraoxonases: role in human diseases and methodological difficulties in measurement

Research into the paraoxonase (PON) gene family has flourished over the past few years. In the 1970s and 1980s, only PON1 was known, and the investigations were conducted, essentially, by toxicologists focusing on protection against organophosphate poisoning. Since then, two new members of the family, PON2 and PON3, have been identified, both being shown to play antioxidant and anti-inflammatory roles. Evidence exists indicating that the PON family is central to a wide variety of human illnesses such as cardiovascular disease, diabetes mellitus, metabolic syndrome, obesity, non-alcoholic steatohepatitis, and several mental disorders. However, research is hampered considerably by the methods currently available to measure the activity of these enzymes. In this review, we summarize the state of knowledge on PON biochemistry and function, the influence of genetic variations, and the involvement of PON in several diseases. The problems associated with PON measurement, such as sample acquisition, lack of reference methods, and variety of substrates, will be presented. Also, we cover some of the present lines of research and propose some others for future progress in this field.

Association of ACE I/D gene polymorphism with vascular dementia: a meta-analysis

BACKGROUND

Vascular dementia is the second common cause of dementia, only second to Alzheimer's disease in later life, and has a greater mortality risk than Alzheimer's disease among the elderly population group. The angiotensin-converting enzyme insertion/deletion polymorphism as a risk factor in vascular dementia has been suggested, but direct evidence from genetic association studies remain inconclusive. We performed a meta-analysis pooling data from all relevant studies in order to determine the effect of the insertion/deletion polymorphism on the vascular dementia.

METHODS

We applied a random-effects model or fixed-effects model to combine odds ratio and 95% confidence intervals. Q statistic was used to evaluate the homogeneity, and Egger's test and Funnel plot were used to assess publication bias.

RESULTS

A total of 10 studies were included worldwide. Publication bias was not observed. There was no evidence of the association of angiotensin-converting enzyme insertion/deletion polymorphism with the vascular dementia in general or in the Asian populations or in the Caucasian populations.

CONCLUSIONS

The angiotensin-converting enzyme insertion/deletion polymorphism might be neutral to vascular dementia.

Methylenetetrahydrofolate reductase gene and risk of Alzheimer's disease in Koreans

BACKGROUND

The association between methylenetetrahydrofolate reductase (MTHFR) c.677C>T (A222V) polymorphism and Alzheimer's disease (AD) is controversial. The objectives of the study were to investigate the association between MTHFR c.677C>T polymorphism and AD in Korean elders and to the extent to which it is modified by the major components of one-carbon metabolism and apolipoprotein E (APOE) genotype.

METHODS

Seven hundred and thirty-two community residents aged 65 or over were clinically assessed for AD. Genotyping was performed for MTHFR c.677C>T and APOE; serum levels of folate, vitamin B(12), and homocysteine were assayed. Age, gender and education were included as covariates.

RESULTS

A trend of association between TT genotype of MTHFR c.677C>T and AD was found [adjusted OR (95% CI): 1.73 (0.80-3.74)]. The association was significant in the presence of below-median vitamin B(12) level [3.66 (1.14-11.71)] and in APOE e4 non-carriers [2.97 (1.00-8.55)] with significant interaction terms, and bordered on significance in the presence of above-median homocysteine level [2.73 (0.94-7.90)].

CONCLUSIONS

These findings suggest gene-environment and gene-gene interactions on the risk of AD in Koreans.

Pharmacogenomics in Alzheimer's disease

Pharmacological treatment in Alzheimer's disease (AD) accounts for 10-20% of direct costs, and fewer than 20% of AD patients are moderate responders to conventional drugs (donepezil, rivastigmine, galantamine, memantine), with doubtful cost-effectiveness. Both AD pathogenesis and drug metabolism are genetically regulated complex traits in which hundreds of genes cooperatively participate. Structural genomics studies demonstrated that more than 200 genes might be involved in AD pathogenesis regulating dysfunctional genetic networks leading to premature neuronal death. The AD population exhibits a higher genetic variation rate than the control population, with absolute and relative genetic variations of 40-60% and 0.85-1.89%, respectively. AD patients also differ in their genomic architecture from patients with other forms of dementia. Functional genomics studies in AD revealed that age of onset, brain atrophy, cerebrovascular hemodynamics, brain bioelectrical activity, cognitive decline, apoptosis, immune function, lipid metabolism dyshomeostasis, and amyloid deposition are associated with AD-related genes. Pioneering pharmacogenomics studies also demonstrated that the therapeutic response in AD is genotype-specific, with apolipoprotein E (APOE) 4/4 carriers the worst responders to conventional treatments. About 10-20% of Caucasians are carriers of defective cytochrome P450 (CYP) 2D6 polymorphic variants that alter the metabolism and effects of AD drugs and many psychotropic agents currently administered to patients with dementia. There is a moderate accumulation of AD-related genetic variants of risk in CYP2D6 poor metabolizers (PMs) and ultrarapid metabolizers (UMs), who are the worst responders to conventional drugs. The association of the APOE-4 allele with specific genetic variants of other genes (e.g., CYP2D6, angiotensin-converting enzyme [ACE]) negatively modulates the therapeutic response to multifactorial treatments affecting cognition, mood, and behavior. Pharmacogenetic and pharmacogenomic factors may account for 60-90% of drug variability in drug disposition and pharmacodynamics. The incorporation of pharmacogenetic/pharmacogenomic protocols to AD research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety.

Alzheimer's disease in Brazilian elderly has a relation with homocysteine but not with MTHFR polymorphisms

OBJECTIVE: To investigate the association between total plasma homocysteine concentration, C677T and A1298C polymorphisms in MTHFR gene and Alzheimer's disease (AD) development. METHOD: Forty-three patients with probable (63%) and possible (37%) AD and 50 non-demented controls were evaluated. Groups did not differ as to gender, age, scholar years, diabetes, alcohol and coffee intake and physical activity. Total plasma homocysteine (Hcy) levels were determined by HPLC and genotyping for MTHFR by PCR/RFLP. Mann-Whitney "U" test was used to compare quantitative variable, Fisher-Freeman-Halton test to compare genotypes and allele proportions and Chi-square test to other qualitative variables. RESULTS: AD patients presented higher total plasma Hcy levels than controls and the difference was statistically significant. No differences in the C677T and A1298C MTHFR polymorphisms distributions were found between patients and controls. Plasma homocysteine concentration did not change with MTHFR genotypes. CONCLUSION: Our data confirms the association between increased plasma Hcy concentration and AD and suggests that neither C677T nor A1298C MTHFR polymorphisms contributed to genetic susceptibility for AD in elderly individuals in the Northeast of Brazil.

Association analysis of the paraoxonase-1 gene with Alzheimer's disease

Genetic variants in the paraoxonase (PON) gene cluster, particularly a single C/T promoter polymorphism (rs 705381) in the PON-1 gene, have recently been associated with Alzheimer's disease (AD). The T allele, in particular, presents an increased risk for the development of AD. Here, we investigate the potential role of this polymorphism in an Italian case-control population consisting of 306 sporadic AD patients and 275 controls, and also evaluate a possible interaction with the ApoE genotype. No association between the PON-1 polymorphism and AD was observed. The T allele frequency was slightly over-represented in AD patients compared to the controls, but this was far from being statistically significant. Our sample was evaluated to have 97.3% power to detect an OR of 2.0 (64.3% power with OR=1.5) at an alpha level of 0.05. No evidence of an interaction between the T risk-allele and the ApoE epsilon4 allele status and no effect of the PON-1 polymorphism on age at onset was detected. Our results do not support other studies indicating that the PON-1 promoter polymorphism plays a major role in AD, suggesting that other large studies are necessary to further elucidate the effect of PON on the development of the disease in the general population.

Apolipoprotein E, angiotensin-converting enzyme and kallikrein gene polymorphisms and the risk of Alzheimer's disease and vascular dementia

Lipoproteins and vascular factors may play roles in the development of Alzheimer's disease (AD) and/or vascular dementia (VaD). In this study, odd ratios (ORs) and 95% confidence intervals (CIs) for apolipoprotein E (APOE), angiotensin-converting enzyme (ACE), and kallikrein (KLK1) polymorphisms were computed to test their association with the disease by a case-control study. The risk of AD was significantly increased for individuals with APOE varepsilon4 allele (OR = 3.73, 95% CI = 2.38-5.98). The risk of AD was also significant for people with ACE DD genotype, D allele, or T-D haplotype [OR (95% CI) = 4.29 (1.96-10.23), 1.90 (1.35-2.70), or 2.91 (1.71-5.10), respectively]. The above association between ACE-VaD was also strong (p = 0.0012, 0.0050, 0.0007, respectively). Reporter constructs containing the -240 A or T allele displayed similar transcriptional activity in both HEK-293 and IMR-32 cells. Thus, another putative pathogenic marker that is linked with the Alu D allele might affect the risk of AD and VaD in Taiwan.

Polymorphisms in the PON gene cluster are associated with Alzheimer disease

Paraoxonase is an arylesterase enzyme that is expressed in the liver and found in the circulation in association with apoA1 and the high-density lipoprotein, and prevents the accumulation of oxidized lipids in low-density lipoproteins in vitro. Common polymorphisms in genes encoding paraoxonase are established risk factors in a variety of vascular disorders including coronary artery disease and carotid artery stenosis, but their association with Alzheimer disease (AD) is controversial. We tested the association of 29 SNPs in PON1, PON2 and PON3 with AD in 730 Caucasian and 467 African American participants of the MIRAGE Study, an ongoing multi-center family-based genetic epidemiology study of AD. Eight SNPs were associated with AD in the African American families (0.0001< or =P< or =0.04) and two SNPs were associated with AD in Caucasian families (0.01< or =P< or =0.04). Of note, the pattern of association for the PON1 promoter SNP -161[C/T] was the same in both ethnic groups (P=0.006). Haplotype analysis using sliding windows revealed 11 contiguous SNP combinations spanning the three PON genes with significant global test scores (0.006< or =P< or =0.04) in the two ethnic groups combined. The most significantly associated haplotype comprised SNPs in the region spanning the -161[C/T] SNP (P=0.00009). Our results demonstrate association between AD and variants in the PON gene cluster in Caucasians and African Americans.

Association of MTHFR gene polymorphism C677T with susceptibility to late-onset Alzheimer's disease

Increased total plasma homocysteine (t-Hcy) levels are found to be associated with Alzheimer's disease (AD). Because the methylenetetrahydrofolate reductase (MTHFR) gene encodes a key enzyme that influences the metabolism of homocysteine, it has been considered as a possible genetic risk factor for AD. Although the MTHFR gene C677T polymorphism has a significant impact on reducing enzyme activity and increasing t-Hcy concentrations, the association between the C677T polymorphism and AD remains inconclusive. To determine whether the MTHFR gene C677T polymorphism contributes to the risk for late-onset AD (LOAD) in Chinese, we have investigated 104 sporadic LOAD patients and 130 healthy controls. The strong associations of the TT genotype and T-allele with LOAD (p 0.001, OR 5.73 95% CI 1.85-17.72, and p 0.002, OR 1.89 95% CI 1.25-2.86) were found. After stratifying by apolipoprotein E allele 4 (APOE epsilon4) status, increased LOAD risks associated with the TT genotype only in the APOE epsilon4 noncarriers (chi2=8.92, df=1, p=0.003) and with the T-allele in either group (chi2=5.18, df=1, p=0.023 and chi2=5.53, df=1, p=0.019) were seen. These results suggest that as an APOE epsilon4 allele-dependent risk factor, the MTHFR gene C677T polymorphism is involved in developing LOAD in Chinese.

Large meta-analysis establishes the ACE insertion-deletion polymorphism as a marker of Alzheimer's disease

Apolipoprotein E epsilon4 (APOE*4) is the only fully established susceptibility allele for Alzheimer's disease. One of the most studied candidates is the insertion (I)/deletion (D) polymorphism (indel) of the gene for angiotensin I-converting enzyme (ACE). This study aimed to clarify its association with Alzheimer's disease. The meta-analysis included 39 samples, comprising 6,037 cases of Alzheimer's disease and 12,099 controls, using mainly primary data. Potential interactions with gender, age, ethnic group, and carrier status of the apolipoprotein E epsilon4 allele were all examined. D homozygotes were at reduced risk of Alzheimer's disease (odds ratio = 0.81, 95% confidence interval: 0.72, 0.90; corrected p = 0.0004); I homozygotes showed no association with Alzheimer's disease, while heterozygotes were at increased risk. Although there were clear differences among the three ethnic groups examined (North Europeans, South Caucasians, and East Asians), in all groups D homozygotes were at reduced risk. These results confirm the association of the angiotensin I-converting enzyme indel with Alzheimer's disease across diverse populations, although this is probably due to linkage disequilibrium with the true risk factor. Further, in North Europeans, both association and Hardy-Weinberg analysis suggested partial heterosis, that is, an increased risk for heterozygotes, due to a hidden interaction with another, as yet unknown, risk factor. This interaction warrants further investigation.

Lack of association between angiotensin-converting enzyme and dementia of the Alzheimer's type in an elderly Arab population in Wadi Ara, Israel

The angiotensin-converting enzyme (ACE), a protease involved in blood pressure regulation, has been implicated as an important candidate gene for Alzheimer's disease (AD). This study investigated whether the ACE gene insertion-deletion (ID) polymorphism is associated with risk of developing dementia of Alzheimer's type (DAT) in an Arab-Israeli community, a unique genetic isolate where there is a high prevalence of DAT. In contrast to several other studies, we found no evidence of an association between this polymorphism and either DAT or age-related cognitive decline (ARCD).

ACE I/D polymorphism is a risk factor of Alzheimer's disease but not of vascular dementia

Different studies have investigated the effect of the angiotensin converting enzyme (ACE) insertion/deletion (I/D) polymorphism on the risk of Alzheimer dementia (AD). However, results on the association of the ACE-I allele with AD have been inconclusive. A recent meta-analysis reported an association of the I-allele with the risk of AD. A few small studies also investigated the effect of ACE polymorphism on the risk of vascular dementia (VD). We have investigated the effect of ACE I/D polymorphism in 351 AD and 155 VD patients and 348 healthy controls. We found the I/I genotype to be associated with an increased risk of AD, but not with the risk of VD. Cell-specific effects of ACE polymorphism are suggested, additional studies on neuronal cells might help to understand the role of this polymorphism in AD.

ACE gene is associated with Alzheimer's disease and atrophy of hippocampus and amygdala

Despite biological support for a role of angiotensin converting enzyme (ACE) in Alzheimer's disease (AD), studies assessing the ACE I/D polymorphism in AD are conflicting. We re-evaluated this association in the Rotterdam Study, a population-based cohort study. The mechanism of association was further explored by adjusting for vascular factors, and by analysing atrophy, white matter lesions and infarcts on MRI in non-demented individuals. Genotypes were available for 6488 participants. During average follow-up of 6 years 250 subjects developed AD. MRI data were available for 494 non-demented participants. Homozygosity for the I-allele conferred a slightly increased risk of AD compared to carrying a D-allele (RR 1.12 (95% CI 0.99-1.25)). This increase was only significant in women, and independent of vascular factors (RR 1.39 (95% CI 1.14-1.69)). Non-demented women with the II genotype had smaller hippocampal and amygdalar volumes. Vascular pathology was not significantly associated with ACE. This suggests a modest but significant increase in risk of AD and early AD pathology in women homozygous for the ACE I-allele independent of vascular factors.

ACE genotype and cognitive decline in an African-Caribbean population

The insertion/deletion (I/D) polymorphism of the angiotensin I converting enzyme (ACE) gene is believed to influence risk of cerebrovascular disease. However, associations with cognitive outcomes remain controversial. As far as we are aware, all studies to date have been carried out in white American or European populations. African-Caribbean populations have high prevalence rates of hypertension, diabetes and cerebrovascular disease but risk factors for cognitive outcomes remain under-researched. In a UK community sample of 148 African-Caribbean people aged 55-75 years, we investigated the association between ACE genotype and cognitive decline over 3 years using a battery of repeated tests. No direct association was found between ACE genotype and decline. However, the association between increased age and cognitive decline was significantly stronger in people with the ACE DD genotype (odds ratio 3.6 per 5-year increase, 95% CI: 1.9-6.7) compared to those with ID/II genotype (odds ratio 0.7, 95% CI 0.4-1.2). This interaction was particularly strong for decline in verbal memory and was not apparently mediated by vascular risk factors measured at baseline.

Methylenetetrahydrofolate reductase and angiotensin converting enzyme gene polymorphisms in two genetically and diagnostically distinct cohort of Alzheimer patients

The role of methylenetetrahydrofolate reductase (MTHFR) and angiotensin converting enzyme (ACE) gene polymorphisms as risk factors for the occurrence of Alzheimer's disease (AD) is still controversial. In this study, we investigated the common MTHFR C677-->T and ACE insertion/deletion (I/D) gene polymorphisms as risk factors for AD in two genetically and diagnostically distinct cohort of Alzheimer's patients. We analyzed a neuropathologically confirmed American cohort of 124 AD patients and 97 elderly controls, and a clinically diagnosed Italian cohort of 126 probable AD cases, 106 elderly controls, and a community-based sample of 1232 subjects aged under 65 years. No difference was found in polymorphism distribution between cases and controls in both study cohorts. We also tested a possible association between the polymorphisms investigated. No interaction was found between the MTHFR and ACE alleles. Moreover, no association was found for the ACE and MTHFR polymorphisms with age at onset, disease duration and MMSE score at observation. Thus, in our study, MTHFR C677-->T and ACE I/D polymorphisms do not appear to confer an added risk for AD.

Paraoxonase gene polymorphisms, oxidative stress, and diseases

The paraoxonase (PON) gene cluster contains at least three members, including PON1, PON2, and PON3, located on chromosome 7q21.3-22.1. Until now there has been little insight into the role of the respective gene products in human physiology and pathology. However, emerging evidence from biochemical and genetic experiments is providing clues about the role(s) of the products of these genes, which indicates that PON(s) acts as important guardians against cellular damage from toxic agents, such as organophosphates, oxidized lipids in the plasma low-density lipoproteins. In parallel, substantial data have been published on the association between the polymorphisms of PON(s) and coronary heart disease. It has become clear that the polymorphisms significantly affect the prevalence of coronary heart disease. However, the associations between the PON(s) polymorphisms and most of these conditions were found to be inconsistent when additional populations were investigated. This contribution provides an overview of the status of research of each of the three genes and the available association studies and the potential problems in interpreting the data. We also review the current evidence on the association between PON(s) polymorphisms and diseases other than coronary heart disease and some metabolic quantitative phenotypes, such as plasma lipoproteins, plasma glucose, and birthweight. Finally, we suggest directions for the future that might elucidate the role of the PON genetic polymorphisms in this potentially important function of PON(s) and the role in coronary heart disease and other related diseases.

The renin-angiotensin-aldosterone system and Alzheimer s disease?

Epidemiological studies from the last decade have begun to produce evidence that the perceived joint occurrence of vascular disease and Alzheimer's disease (AD), both common elderly disorders more often believed to occur by chance due to their high prevalence, may now actually have a more pathological significance. The following review discusses some of this evidence and the implications for cognitive decline and the development of AD and how a well-known cardiovascular risk factor gene, the apolipoprotein E (APOE) gene, plays a significant role in the molecular genetics of AD. It also introduces and discusses recent and compelling evidence for the involvement of another well-known cardiovascular risk factor gene, the angiotensin-converting enzyme (ACE1) gene, in the pathogenesis of AD. This role is suggested in terms of recent molecular genetic association evidence implicating the ACE1 insertion/deletion (indel) polymorphism, a more recent large haplotype study that greatly extends the ACE1 indel evidence and incorporates knowledge accrued from previous cardiovascular disease-focused ACE1 haplotype studies. Finally, this paper discusses very recent biological evidence that further supports a role for ACE1 and hypothesises a number of readily testable mechanisms by which the ACE1 enzyme and other components of the renin-angiotensin-aldosterone system may be implicated in increased risk and/or the progression of AD.

Variation in the DCP1 gene, encoding the angiotensin converting enzyme ACE, is not associated with increased susceptibility to Alzheimer's disease

OBJECTIVES

To attempt to replicate previous reports that polymorphic variation in the DCP1 gene causes increased susceptibility to the development of Alzheimer's disease, either on its own or in interaction with the effects of the gene for apolipoprotein E (APOE).

METHOD

Subjects older than 65 years of age consisting of 81 dementia patients diagnosed as having possible or probable Alzheimer's disease and 68 controls were obtained from Camden, Islington and Harlow psychiatric services. Subjects were genotyped for APOE alleles e2, e3 and e4, and the common insertion/deletion polymorphisms for DCP1* I/D were genotyped.

RESULTS

There was no statistically significant difference in the frequency of the DCP1* insertion/deletion alleles between the cases and controls (X2 =0.04, 1 degree of freedom, not significant). When subjects were subdivided according to whether they possessed at least one copy of the APOE e4 allele, there were still no differences in DCP1 allele frequencies between cases and controls.

CONCLUSIONS

Further research is needed to elucidate any role that the DCP1 polymorphism may play in relation to Alzheimer's disease. Previous studies may be false positive, or inconsistency in replication may be due to heterogeneity.

Lack of association between angiotensin converting enzyme polymorphism and sporadic Alzheimer's disease

Epidemiological and pathogenetic evidences suggest a strong association between vascular risk factors and sporadic Alzheimer's disease (sAD). In agreement with the vascular hypothesis of AD, the role of various candidate genes for atherosclerosis has been investigated, leading to conflicting results. In order to clarify the significance of angiotensin-converting enzyme (ACE) gene insertion (I)/deletion (D) polymorphism in a group of patients with sAD, we conducted a case-control study including 149 cases and 149 age and sex matched controls. All subjects were genotyped for ACE and Apolipoprotein E (APOE). There were no significant differences in ACE genotype or allele frequencies between cases and controls, even after stratification for APOE4 carrier status. Our data suggest that the ACE I/D polymorphism is not associated to genetic susceptibility in sAD patients.

APOE genotype in cerebrovascular disease and vascular dementia

BACKGROUND

The fact that the allele epsilon 4 of the Apolipoprotein E (APOE) gene could act like a risk factor not only in late-onset familial and sporadic Alzheimer's disease (AD) but also in cerebrovascular disease (CVD) and vascular dementia (VaD) is still controversial.

METHODS

In order to study if epsilon 4 allele is overrepresented not only in AD but also in CVD and VaD, APOE genotyping was undertaken in a series of 247 patients: 26 cases with VaD, 41 cases with CVD but without cognitive impairment (CVD-C), 83 cases with AD and 97 aged-matched "healthy controls" (HC).

RESULTS

Percentages of subjects bearing one or two copies of the epsilon 4 allele was much higher in AD patients (54%) than in either CVD-C (29%) (p<0.05), VaD (15%) (p<0.001) or HC (13%) (p<0.001).

CONCLUSIONS

These results strengthen the hypothesis that involves the APOE epsilon 4 allele as a predisposing factor for AD, but not for CVD or VaD.